This invention relates to brushless d-c motors in general, and more particularly to such a motor having improved performance.
Brushless d-c motors with several Y connected phase windings, which can be connected to a d-c voltage source via a commutation arrangement consisting of controlled semiconductor elements, with each phase winding having its winding end which is connected to the controlled semiconductor element connected to the one terminal of a pickup diode and the pickup diodes having their other terminals connected to a common tie point, are known. In order to prevent, on the one hand, destruction of the controlled semiconductor elements of the commutation arrangement by the self-induction voltage occurring when the individual phase windings are switched off, and to counteract, on the other hand, falsification of the actual speed value by this self-induction voltage, a voltage-dependent element has its one terminal connected to the common tie point of the pickup diodes and its other terminal connected, via a series resistor, to the neutral point of the phase windings. The load circuit of a controlled semiconductor switching element is shunted across the voltage-dependent element and the series resistor, and the actual speed value is taken off via a smoothing member consisting of at least a resistor and a capacitor between the neutral point and the common tie point of the pickup diodes.
It has been found that particularly in motors with a slotted stator, motor current dependent components are superimposed on the speed-proportional e.m.f. which is picked up via the diodes. This results in a load dependent speed error for the drive, which falsifies the actual speed value.